Synthesis of azobenzenes: the coloured pieces of molecular materials

Azobenzenes are ubiquitous motifs very important in many areas of science. Azo compounds display crucial properties for important applications, mainly for the chemical industry. Because of their discovery, the main application of aromatic azo compounds has been their use as dyes. These compounds are excellent candidates to function as molecular switches because of their efficient cis-trans isomerization in the presence of appropriate radiation. The classical methods for the synthesis of azo compounds are the azo coupling reaction (coupling of diazonium salts with activated aromatic compounds), the Mills reaction (reaction between aromatic nitroso derivatives and anilines) and the Wallach reaction (transformation of azoxybenzenes into 4-hydroxy substituted azoderivatives in acid media). More recently, other preparative methods have been reported. This critical review covers the various synthetic methods reported on azo compounds with special emphasis on the more recent ones and their mechanistic aspects (170 references).     

A highly active nano-palladium catalyst for the preparation of aromatic azos under mild conditions

A worm-like Pd nanocatalyst has been prepared and used in the preparation of azo compounds from nitroaromatics under mild reaction conditions. This highly dispersible nano-Pd catalyst shows high activity toward the synthesis of both symmetric aromatic azo compounds and a range of asymmetric aromatic azo compounds.     

Solution and solid state structure and tautomerism of azo coupled enaminone derivatives of benzoylacetone

The reaction of 4-substituted benzenediazonium tetrafluoroborates with 3-amino-1-phenylbut-2-en-1-one, 4-amino-4-phenylbut-3-en-2-one and their N-aryl derivatives 1a-1g has been used to prepare the respective azo coupling products i.e. compounds 2-5 from enaminone 1a, compounds 6-9 from enaminone 1c, compound 10 from enaminone 1d, compound 11 from enaminone 1e, compounds 12, 13 from enaminone 1f, compounds 14, 15 from enaminone 1b and compound 16 from enaminone 1g. Tautomerism of the azo coupling products prepared has been investigated in CDCl3 solutions by means of 1H, 13C and 15N NMR spectra. Crystal structures of selected products have also been investigated by means of X-ray diffraction.     

Synthesis and reactions of oxo and thio derivatives of 1,3-thiazane

The reaction of 1,3-thiazane-2,4-dithione with amino compounds and diazonium salts has given the corresponding 4- and 5-substituted derivatives. The high reactivity of the thione group in position 4 has been noted. The optimum conditions for azo coupling have been found.For part II, see [1].     

A Simple,Efficient and New Method for Preparing N-Aryl-2-Phenyldiazenecarboxamide

Using ferric chloride to oxidize aryl substituted semicarbazide for preparing azo compounds has been described for the first time in this paper. Nine azo compounds have been synthesized in a good to excellent yield (≥88%). This method only needs cheap reagents, simple instruments and a short reaction time.     

A Convenient,Rapid and New Catalyst Oxidation Method with KClO3/H2SO4/FeSO4 for Preparing Aryl Azo Compounds

Using potassium chlorate, sulfuric acid and ferrous sulfate as a catalytic oxidation system to oxidize the aryl substituted semicarbazide to prepare azo compounds in one phase have been described first time in this paper. Fourteen azo compounds have been synthesized in excellent yields(>90%). This method only needs cheap reagents, simple instrument and short reaction time. A possible mechanism has been suggested.     

Enantiopure sulfinyl azobenzenes as chiroptical switches

[reaction: see text] Photoswitchable enantiopure sulfinyl azo compounds have been synthesized. A remarkable perturbation of the azo system by the stereogenic sulfinyl moiety has been observed by CD in both the trans and the cis azobenzenes resulting by photoisomerization. After five irradiation cycles, the configurational integrity of these chiral switches remains unchanged.     

An Experimental and Theoretical Study on Influence of H‐bonding on the Synthesized Azo Derivatives Structures

We have reported a simple and efficient reaction for the synthesis of some new functionalized azo structures which were prepared by electron deficient acetylenic compounds in the presence of triphenylphosphine. The characterization of the synthesized azo compounds has been determined by FTIR, UV‐Vis, ¹H NMR, ¹³C NMR and Mass spectroscopic techniques. The influence of H‐bonding on the products has been shown by different experimental analysis. Also, the regioselectivity of the reaction, tautomerization equilibrium and the stability of products was investigated using DFT calculations at the B3LYP/6‐31G level of theory.     

N,2-二芳基二氮亚烯甲酰胺合成的新方法

偶氮化合物可用作非线性光学材料、激光盘信息存贮材料和现代科技中的油溶性染料［１］．传统偶氮化合物的制备有重氮盐偶合和取代肼氧化等许多方法［２～４］,其偶氮基两端一般联有烃基或芳环,而联有羰基的偶氮类化合物用通常方法难以制备．本文首次用Ｎ－溴代丁二酰亚...     

羟基喹啉偶氮类化合物的互变异构与顺反异构的研究

本工作合成了数种带不同取代苯基的羟基喹啉偶氮类化合物。对它们在不同溶剂。不同酸碱度溶液中的偶氮式及腙式间互变异构平衡进行了研究。苯环上不同取代基的引入可引起平衡发生变化。拉电子基的引入有利于腙式结构的形成,而推电子基的引入则对偶氮的生成影响不大。此外,工作中还发现:羟基喹啉偶氮化合物在光照下存在着以偶氮顺-反异构化反应为主的变化过程。     

Phase Transfer Catalyzed Dehydrogenation Synthesis of Azo Ureas From Aryl Substituted Semicarbazide

Phase transfer catalyzed dehydrogenation synthesis azo Ureas Compounds have been studied. Ten of the compounds were Synthesized by the reaction of aryl Substituted Semicarbazied Compounds with phase transfer catalyst–“Galvinoxyl” radical between two phase under mild Conditions. The products are obtained in 90–99(%) yield. Their structure are identified by elemental analysis, IR, ¹HNMR, MS spectra. A possible mechanism is suggested by a “Galvinoxyl” radical act on aryl substituted semicarbazide formed azo compounds.

Synthesis of bis (Substituted phenyl) Carbodiazone Compounds (ArN = NCON = NAr') have been reported¹, As another part of our studies, 1, 4-di-Substituted azo Compounds (ArNHCON=NAr') Were Synthesized by the reaction of Substituted Semicarbazide Compounds With a phase transfer Catalyst-“Galvinoxyl” radical, which has been acted as a radical Scavenger², yet, “Galvinoxyl” radical used as phase transfer Catalyst have not been reported so far. Azo Compounds have been widely utilized as dyes and analytical reagents. They can also be used as material of non - linear optics, optic information storring material in Laser dish and dyes with oil solubility in photochromy in modern technology^3,4. Recently, many noteworthy Studies show that azobenzene derivative Possess Very good optic remembering and photoelectric properties⁵, optical Switching and Image storege by means of Azobenzene Liquid - Crystal Films⁶. The preparation of the azo compounds which have the Connection of -N = N- and hydrocarbyl group have been described in many Literatures^7,8.. In this paper, a new reaction of phase transfer Catalyzed dehydrogenation of aryl Substituted Semicarbazide     

硝普钠与苯肼的反应

有氧存在下 ,硝普钠 (Na2 [Fe(CN) 5NO] )与苯肼类化合物在N ,N 二甲基甲酰胺中作用 ,发生脱肼反应 ,生成叠氮苯、苯衍生物、微量的苯胺及偶氮化合物 .对可能的反应机理进行了讨论     

相转移催化合成偶氮脲

取代氨基脲的两相转移催化脱氢合成偶氮脲是一种新反应, 本文报道了用2, 4, 6-三叔丁基苯酚两相转移催化取代氨基脲脱氢形成偶氮化合物, 在温和的条件下合成了10个新偶氮脲, 均获得较好的产率(88-99%), 并对其反应机理作了合理的解释。     

Synthesis,characterization, and dyeing performance of some azo thienopyridine and thienopyrimidine dyes based on wool and nylon

A string of novel heterocyclic mono azo dyes were synthesized and their utilization in dyeing different fabrics as wool and nylon were discussed. Thienopyridine azo dyes 4 and 6 were prepared by reaction of chloro acetamidederivative 2 with diamino compounds to yield 3 and 5 , followed by reaction with NaNO₂/HCl and coupling with nucleophilic reagent. One-pot reaction of chloro acetamide 2 with ammonium thiocyanat in solvent ethanol gave the unexpected thienopyrimidine derivative 7 , which contain two active sites, the former is primary amine that was able to form diazonium salt that coupled with N,N-dimethylaniline, resorcinol, and/or self-coupling to afford the azo dyes 8-10 , and the latter is active methylene group that underwent coupling with different diazonium salts to give the azo thienopyrimidine derivative dye 11-15 . The dyeing performance of these azo dyes had been investigated in terms of their dyeing behavior and fastness properties on different fabrics. Results showed that the color strength (K/S) values, as well as, washing, rubbing, and resistance to acid, alkali and light showed high efficiency of these heterocyclic mono azo dyes to dye wool rather than nylon fibers.     

An Efficient Solid-State Synthesis of N-Aryl-2-phenyldiazenecarboxamides

The subject of organic solid-state synthesis is a fascinating one. It has many advantages such as high efficiency and selectivity, easy separation and purification, mild reaction conditions, and environmental acceptability1. In recent years, this method has been widely used in a variety of organic reactions including substitution2, condensation3, oxidation-reduction4, rearrangement5 and elimination6. However, the solid state reaction using K3Fe(CN)6/KOH to oxidize substituted semicarbazides…     

Alkoxyl- and carbon-centered radicals as primary agents for degrading non-phenolic lignin-substructure model compounds

Lignin degradation by white-rot fungi proceeds via free radical reaction catalyzed by oxidative enzymes and metabolites. Basidiomycetes called selective white-rot fungi degrade both phenolic and non-phenolic lignin substructures without penetration of extracellular enzymes into the cell wall. Extracellular lipid peroxidation has been proposed as a possible ligninolytic mechanism, and radical species degrading the recalcitrant non-phenolic lignin substructures have been discussed. Reactions between the non-phenolic lignin model compounds and radicals produced from azo compounds in air have previously been analysed, and peroxyl radical (PR) is postulated to be responsible for lignin degradation (Kapich et al., FEBS Lett., 1999, 461, 115-119). However, because the thermolysis of azo compounds in air generates both a carbon-centred radical (CR) and a peroxyl radical (PR), we re-examined the reactivity of the three radicals alkoxyl radical (AR), CR and PR towards non-phenolic monomeric and dimeric lignin model compounds. The dimeric lignin model compound is degraded by CR produced by reaction of 2,2'-azobis(2-amidinopropane) dihydrochloride (AAPH), which under N(2) atmosphere cleaves the α-β bond in 1-(4-ethoxy-3-methoxyphenyl)-2-(2-methoxyphenoxy)-1,3-propanediol to yield 4-ethoxy-3-methoxybenzaldehyde. However, it is not degraded by the PR produced by reaction of Ce(4+)/tert-BuOOH. In addition, it is degraded by AR produced by reaction of Ti(3+)/tert-BuOOH. PR and AR are generated in the presence and absence of veratryl alcohol, respectively. Rapid-flow ESR analysis of the radical species demonstrates that AR but not PR reacts with the lignin model compound. Thus, AR and CR are primary agents for the degradation of non-phenolic lignin substructures.     

Effect of cooperative hydrogen bonding in azo-hydrazone tautomerism of azo dyes

Azo-hydrazone tautomerism in azo dyes has been modeled by using density functional theory (DFT) at the B3LYP/6-31+G(d,p) level of theory. The most stable tautomer was determined both for model compounds and for azo dyes Acid Orange 7 and Solvent Yellow 14. The effects of the sulfonate group substitution and the replacement of the phenyl group with naphthyl on the tautomer stability and on the behavior in solvent have been discussed. Intramolecular hydrogen bond energies have been estimated for the azo and hydrazone tautomers to derive a relationship between the tautomer stability and the hydrogen bond strength. The transition structures for proton transfer displayed resonance assisted strong hydrogen bonding properties within the framework of the electrostatic-covalent hydrogen bond model (ECHBM). Evolution of the intramolecular hydrogen bond with changing structural and environmental factors during the tautomeric conversion process has been studied extensively by means of the atoms-in-molecules (AIM) analysis of the electron density. The bulk solvent effect was examined using the self-consistent reaction field model. Special solute-solvent interactions were further investigated by means of quantum mechanical calculations after defining the first-solvation shell by molecular dynamics simulations. The effect of cooperative hydrogen bonding with solvent molecules on the tautomer stability has been discussed.     

Addition of arylboronic acids to symmetrical and unsymmetrical azo compounds

[reaction: see text] The addition of aryl- and heteroarylboronic acids to azo compounds is described. Copper salt catalysis was necessary to perform the reaction under mild conditions and high yields. Excellent regioselectivity was observed in addition to unsymmetrical azo compounds.     

Heterogeneous Suzuki and copper-free Sonogashira cross-coupling reactions catalyzed by a reusable palladium(II) complex in water medium

A new polystyrene anchored Pd(II) azo complex has been synthesized and characterized. The present Pd(II) azo complex behaves as a very efficient heterogeneous catalyst in the Suzuki coupling and Sonogashira coupling reaction in water medium. Aryl halides, coupled with phenylboronic acids (Suzuki-Miyaura reaction) or terminal alkyne (Sonogashira reaction), smoothly afford the corresponding cross-coupling products in excellent yields (83-100% yield for Suzuki reaction and 68-96% yield for Sonogashira reaction of aryl halides) under phosphine-free reaction conditions in the presence of polystyrene anchored Pd(II) azo complex catalyst in water medium. Furthermore, the catalyst has shown good thermal stability and recyclability. This polymer-supported Pd(II) catalyst could be easily recovered by simple filtration of the reaction mixture and reused for more than six consecutive trials without a significant loss of its catalytic activity.     

偶氮基杯芳烃化合物的合成及其偶氮-醌腙互变异构性质

通过芳胺的重氮化-偶合反应合成了8个偶氮基杯芳烃化合物, 其结构经IR, 1H NMR, ESI-MS和元素分析表征. 通过UV-Vis, 1H NMR和IR考察了溶液pH值对所合成化合物5,11,17,23-四[(2-苯并噻唑基)偶氮基]-25,26,27,28-四羟基杯芳烃(3)和5,17-二[(1-萘基)偶氮基]-25,26,27,28-四羟基杯芳烃(4)的偶氮-醌腙互变异构的影响. 结果表明, 随着溶液pH值增加, 醌腙体在偶氮-醌腙互变异构平衡中的比例增加, 当pH≥10时, 几乎全部转变为醌腙体. 特别当溶液pH=-1时, 化合物4可以形成一种大的共轭体系, 使其λmax由477 nm红移至545 nm.